Monitoring During anaesthesia

1. Monitoring During anaesthesia Prof. Abdulhamid Al-Saeed, FFARCSI Anaesthesia Department College of Medicine King Saud University

2. Lecture Objectives..Students at the end of the lecture will be able to knows: Monitors : Non-invasive blood pressure , ECG , pulse oximetrycapnography (CO2 monitor) and oxygen analyzer , temperature probe nerve stimulator Specialized monitors : arterial line (invasive blood pressure) central venous line (cvp monitoring) pulmonary artery flotation catheter ( monitors function of right and left side of the heart) BIS monitor (depth of anesthesia)

3. Monitoring: A Definition • interpret available clinical data to help recognize present or future mishaps or unfavorable system conditions

4. Monitoring in the Past • Visual monitoring of respiration and overall clinical appearance • Finger on pulse • Blood pressure (sometimes) Finger on the pulse

5. Monitoring in the Present • Standardized basic monitoring requirements (guidelines) from the ASA (American Society of Anesthesiologists), CAS (Canadian Anesthesiologists’ Society) and other national societies • Many integrated monitors available • Many special purpose monitors available • Many problems with existing monitors (e.g., cost, complexity, reliability, artifacts)

6. Standard ASA monitoring for general anesthesia , monitored anesthesia care and regional anesthesia :- • Oxygenation (oxygen analyzer, pulse oximetry), • Ventilation (capnography, minute ventilation), respiratory rate (under regional anesthesia) • Circulation (electrocardiogram [ECG], arterial blood pressure, perfusion assessment), • Temperature.

7. High Tech Patient Monitoring Examples of Multiparameter Patient Monitors

8. High Tech Patient Monitoring Transesophageal Echocardiography Depth of Anesthesia Monitor Evoked Potential Monitor Some Specialized Patient Monitors

9. Cardiovascular system. The circulatory system is responsible for oxygen delivery to and removal of waste products from the organs, and this must be maintained during anesthesia.

10. Signs and symptoms of perfusion abnormalities • Central nervous system: mental status changes, neurologic deficits. • Cardiovascular system: chest pain, shortness of breath, ECG abnormalities, wall motion abnormalities on echocardiogram. • Renal: decreased urine output, elevated blood urea nitrogen and creatinine, decreased fractional excretion of sodium. • Gastrointestinal: abdominal pain, decreased bowel sounds, hematochezia. • Peripheral: cool limbs, poor capillary refill, diminished pulses.

11. ECG. • The ECG monitors the conduction of electrical impulses through the heart. • Rhythm detection is best seen in lead II.

12. ECG

13. Electrocardiogram • Displays the overall electrical activities of the myocardial cells • Heart rate & dysrhythmias • Myocardial ischaemia • Pacemaker function • Electrolyte abnormalities • Drug toxicity • Does NOT indicate mechanical performance of the heart: • Cardiac output • Tissue perfusion

14. Full (12)-lead ECG • Standard limb leads (bipolar) • Precordial leads (unipolar) • 5.lead system • Unipolar + bipolar • RA, LA, RL, LL, C • 3.lead system • Bipolar with RA, LA, LL • V5 usually used • Best compromise between detecting ischaemia and diagnosing arrhythmia • May come with ST-segment analysis

15. ECG Standard Limb Leads Unipolar Chest Leads

18. Artifacts in ECG Monitoring • Loose electrodes or broken leads • Misplaced leads • Wrong lead system selected • Emphysema, pneumothorax, pericardial effusion • Shivering or restlessness • Respiratory variation and movement • Monitor Pulse Oximetry, Invasive ABP

25. Arterial blood pressure. • Automated noninvasive blood pressure is the most common noninvasive method of measuring blood pressure in the operating room. • Invasive blood pressure monitoring uses an indwelling arterial catheter coupled through fluid-filled tubing to a pressure transducer. • The transducer converts pressure into an electrical signal to be displayed. • Indications • Need for tight blood pressure control (e.g., induced hyper- or hypotension). • Hemodynamically unstable patient. • Frequent arterial blood sampling. • Inability to utilize noninvasive blood pressure measurements.

26. Arterial Blood Pressure

28. Central venous pressure (CVP) and cardiac output • CVP is measured by coupling the intravascular space to a pressure transducer using fluid-filled tubing. • Pressure is monitored at the level of the vena cava or the right atrium. • Indications • Measurement of the right heart filling pressures to assess intravascular volume and right heart function. • Drug administration to the central circulation. • Intravenous access for patients with poor peripheral access. • Indicator injection for cardiac output determination (e.g., green dye cardiac output). • Access for insertion of pulmonary artery catheter. • Range The CVP is normally 2 to 6 mm Hg

29. Central Venous Pressure

32. PULMONARY ARTERY CATHETER

33. Pulmonary Artery Catheter

35. Haemodynamic Profiles Obtained from PA Catheters • SV= CO / HR (60-90 mL/beat) • SVR= [(MAP – CVP) / CO]  80 (900-1500 dynes-sec/cm5) • PVR= [(MPAP – PCWP) / CO]  80 (50-150 dynes-sec/cm5)

36. O2 delivery (DO2) • = C.O.  O2 content • Arterial O2 content (CaO2)= ( Hb  1.38 )  (SaO2) • Mixed venous O2 content (CvO2)= ( Hb  1.38 )  (SvO2) • O2 consumption (VO2)= C.O.  (CaO2-CvO2) • SvO2 = SaO2– [VO2 / (Hb  13.8)(CO)]

37. Respiratory system. • pulse oximetry, capnography, a fraction of inspired oxygen analyzer, and a disconnect alarm. •  Pulse oximeter • combines the principles of oximetry and plethysmography to noninvasively measure oxygen saturation in arterial blood. • The pulse oximeter probe contains two light emitting diodes at wavelengths of 940nm and 660 nm. • Oxygenated and reduced hemoglobin differ in light absorption (940 and 660 nm respectively). • Thus the change in light absorption during arterial pulsation is the basis of oximetry determination. • The ratio of the absorption at the two wavelengths is analyzed by a microprocessor to record the oxygen saturation.

38. Pulse Oximetry

39. Incomptencies • Critically ill with poor peripheral circulation • Hypothermia & VC • Dyes ( Nail varnish ) • Lag Monitor Signalling 5-20 sec • PO2 • Cardiac arrhythmias may interfere with the oximeter picking up the pulsatile signal properly and with calculation of the pulse rate • Abnormal Hb ( Met., carboxy)

40. Capnometry What is Capnometry? • Is the measurement of end-tidal carbon dioxide tension. • This provides valuable information to the anesthesiologist. • The presence of end tidal CO2 aids in confirming endotracheal intubation. • Alteration in the slope of the graph can give clues to the presence of airway obstruction. • A rapid fall in reading may signify extubation, air embolism or low cardiac output with hypovolemia.

41. The Alpha angle The angle between phases II and III, which has increases as the slope of phase III increases. The alpha angle is an indirect indication of V/Q status of the lung. Airway obstruction causes an increased slope and a larger angle. Other factors that affect the angle are the response time of the capnograph, sweep speed, and the respiratory cycle time. The Beta angle The nearly 90 degrees angle between phase III and the descending limb in a time capnogram has been termed as the beta angle. This can be used to assess the extent of rebreathing. During rebreathing, there is an increase in beta angle from the normal 90 degrees.

42. Clinical Applications

44. Central nervous system (level of consciousness) monitoring • Bispectral index (BIS) assess central nervous system depression during general anesthesia. • It is based on the surface electroencephalogram (EEG), which predictably changes in amplitude and frequency as the depth of anesthesia increases.

45. Temperature monitoring Indications Infants and small children are prone to thermal lability due to their high surface area to volume ratio. Adults subjected to large evaporative losses or low ambient temperatures (as occur with exposed body cavity, large volume transfusion of unwarmed fluids, or burns) are prone to hypothermia. Malignant hyperthermia is always a possible complication, and temperature monitoring should always be available.

46. Monitoring site Tympanic membrane temperature Rectal temperature Nasopharyngeal temperature, Esophageal temperature monitoring reflects the core temperature well. The probe should be located at the lower third of the esophagus and rarely may be misplaced in the airway. Blood temperature measurements may be obtained with the thermistor of a PAC.

47. Neuromuscular blockade monitoring: • Neuromuscular blockade is monitored during surgery to guide repeated doses of muscle relaxants and to differentiate between the types of block. • All techniques for assessing neuromuscular blockade use a peripheral nerve stimulator (PNS) to stimulate a motor nerve electrically.

49. 1. Disconnection 2. Hypoventilation 3. Esophageal intubation 4. Bronchial intubation 5. Circuit hypoxia 6. Halocarbon overdose 7. Hypovolemia 8. Pneumothorax 9. Air Embolism 10. Hyperthermia 11. Aspiration 12. Acid-base imbalance 13. Cardiac dysrhythmias 14. IV drug overdose Source: Barash Handbook Detecting Mishaps Using Monitors These mishaps …

50. Pulse oximeter Capnograph Automatic BP Stethoscope Spirometer Oxygen analyzer ECG Temperature 1,2,3,4,5,8,9,11,14 1,2,3,9,10,12 6,7,9,14 1,3,4,13 1,2 5 13 10 Source: Barash Handbook Detecting Mishaps with Monitors … are detected using these monitors